1. Field of the Invention
The present invention relates to a support member mounting a semiconductor element such as a light emitting element and a photodetector, and a semiconductor device employing the support member, and particularly relates to a semiconductor device provided with a high-output and high-luminance semiconductor element mounted thereon and excellent in heat resistance, heat radiation and reliability.
2. Discussion of the Related Art
In recent years, a high-output semiconductor light emitting element such as light emitting diode (LED) and a laser diode (LD) has been developed. Such a semiconductor light emitting element is mounted on a package, which is a support member provided with electrodes for supplying electric power to the semiconductor light emitting element, to assemble a light emitting device.
Examples of a package for hermetically sealing a semiconductor light emitting element such as a light emitting diode and a laser diode include a so-called can package. A can package 5 shown in FIG. 14 as a conventional example comprises a stem 3 having through-holes through each of which an electrode 2 is inserted and fixed via an insulating material, and a cap 6 composed of a light transmitting portion 7 made of glass fitted into a metal ring. A semiconductor light emitting element 1 is disposed to the stem 3 and the electrodes of the semiconductor light emitting element 1 and the electrodes 2 provided to the stem 3 are connected via conductive wires 4. In the can package 5, the semiconductor light emitting element 1 disposed to the stem 3 is hermetically sealed by resistance welding of the stem 3 and the cap 6. That is, one electrode is contacted to the metal ring of the cap 6 and another electrode is contacted to the stem 3 and voltage is applied. By the Joule heat consequently generated, the metal ring of the cap 6 is welded and fixed to the stem 3, so that the semiconductor light emitting element is hermetically sealed. Such a can package 5 is a package excellent in airtightness, in which moisture and the like from the outside is prevented from entering therein.
When producing a semiconductor device having a hermetically sealed semiconductor element, it is preferable to weld the cap to a support member having an insulating substrate provided with a conductive wiring rather than to a metal stem described above. This is because efficient mass-production of the semiconductor devices can be achieved by dividing the substrate into individual support members after welding the caps to the substrate which is a collective of support members to form semiconductor devices.
However, for example, as described in Japanese Laid-open Patent Application No. 2004-200253, in a support member formed by arranging a metal material to an insulating substrate, warpage is generated in the entire body of the support member due to a difference of thermal expansion coefficients between an insulating substrate and a metal material.
Welding a sealing member to the support member having warpage tends to reduce airtightness of the semiconductor device compared with that in the can package where the cap is welded to the metal stem. For example, generation of a gap between a flange portion of the cap and the support member results in a drop in the airtightness of the semiconductor device. When the insulating substrate to which the cap is welded has warpage, stress is concentrated on a specific location of the glass fitted to the cap, and a crack may occur at the specific location and propagate in the glass. Also, when welding the cap to the substrate, due to a pressure exerted from the electrode terminal contacted to the flange portion of the cap, consequent stress derived from the flange portion to the glass may cause a crack in the glass. The airtightness of the semiconductor device is reduced due to the occurrence of the crack in the glass as described above.
In the light emitting device according to Japanese Laid-open Patent Application Publication No. 2004-200253, warpage is reduced by dividing an arrangement region for a metal material joined to the insulating substrate into multiple regions. Even if warpage is thus reduced, sufficient airtightness cannot be obtained in forming a hermetically sealed semiconductor device as described above.
Accordingly, an object of the present invention is to provide a semiconductor device with excellent airtightness, a device in which a semiconductor element is hermetically sealed by a substrate and a sealing member.